1. Field of the Invention
The present invention relates to a shock absorbing jack, intended more particularly, among other applications, for equipping aircraft landing gear, particularly for light aircraft or helicopters and more especially adapted to equipping the main so called pendulum landing gear, the shock absorbing jack being in this latter case disposed in a substantially vertical position and so that the shock absorbing function, that is to say the resilient and damped absorption of the descent energy of the aircraft during landing thereof is fulfilled by compression under load.
Numerous shock absorbing jack constructions have already been proposed for carrying out successively and/or simultaneously the following functions:
(1) the shock absorbing function, when the aircraft lands and/or taxies on the ground, following which the shock absorbing jack also supports the static load formed by the weight of the aircraft, when this latter is motionless on the ground,
(2) the function of raising and lowering the landing gear, when the aircraft is in flight, respectively following take off or before landing, and
(3) the functions of lowering and/or raising the aircraft, also known under the French name of "baraquage" (kneeling) and "contrebaraquage" as well as the return to the normal position, with the undercarriage down, by means of appropriate hydraulic controls, "baraquage" and "contrebaraquage" being defined as operations which consist respectively in lowering or raising the aircraft resting on the ground contact members, such as wheels, with which these landing gear are equipped, beyond the normal position of the aircraft, so as to facilitate certain manoeuvers or to improve certain characteristics of the aircraft.
"Baraqage" in particular facilitates the loading then the transporting of an aircraft in the hold of a cargo carrying aircraft or in a hangar of an aircraft carrying ship. It also improves the stability of said helicopter resting on the deck of a helicopter carrier, aircraft carrier or other ships, even on an offshore platform, because the center of gravity of the helicopter is lowered following lowering thereof, reducing its ground clearance which in addition facilitates anchorage thereof to its parking area.
"Contrebaraquage" of the main landing gear makes it possible in particular to raise the rear of the apparatus and, in the case where this latter is equipped with a rear loading door, to increase the passage height under the tail for loading a vehicle.
2. Description of the prior art
Shock absorbing jacks of this type are described in the French patents and patent applications Nos. 2 340 482, 2 370 196, 2 461 852, 2 493 444 and 2 554 415.
FIG. 1 of French patent No. 2 340 482 shows a shock absorbing jack whose shock absorbing function is fulfilled by compression under load, and which is formed essentially of the following elements:
a shock absorber rod, fixed by its upper end to the structure of the aircraft, and the lower end of which carries a piston with a throttling device with throttling orifices and a flap also pierced with throttling orifices, facing a peripheral chamber defined in the shock absorbing rod which is hollow about an internal cylindrical wall defining a central chamber vented to the atmosphere through a channel passing through the upper end,
a jack rod, which is hollow and whose internal volume is subdivided into two chambers by a transverse dividing wall, so that the part of the jack rod which surrounds the upper chamber forms a shock absorbing body, in which the shock absorber rod is mounted for sliding with sealing by its piston, this upper chamber of the jack rod containing a hydraulic liquid volume which, by passing through the throttling orifices, penetrates into the base of the peripheral chamber of the shock absorbing rod, and the lower end of the jack rod being formed as a jack piston,
a jack cylinder, which is fixed by its lower end to a member of the landing gear carrying the ground contact elements, and in which the jack rod is slidably mounted with sealing by its jack piston, which defines, in the jack cylinder, on the one hand a lowering chamber which, when it is filled with hydraulic liquid, tends to push the jack rod out of the cylinder, so as to bring the landing gear into the undercarriage down position and which, on the other hand, defines with the jack rod and the jack cylinder an annular lifting chamber which, when it is supplied with hydraulic liquid, tends to cause the jack rod to enter the jack cylinder, while emptying the lowering chamber.
Locking of the shock absorbing jack in the "undercarriage down" position is provided either by hydraulic locking of the lowering chamber, filled with hydraulic liquid, or by mechanical locking provided for example by resilient claws carried by the jack cylinder and resiliently clipping behind a step defined by the lower part of the jack rods, a hydraulically controlled locking and unlocking cap being also provided in this case, in the annual lift chamber, so that the hydraulic liquid supply for this latter ensures first of all movement of the locking cap, against a resilient member, into the claw release position then, because of the pressure which develops in the lift chamber, entry of the piston and the jack rod into the jack cylinder, whose lowering chamber is emptied by a discharge valve with opening controlled by the pressurization of the lift chamber. This makes it possible to pass from the undercarriage down position to the undercarriage up position. Passing from the latter to the first of these two positions is obtained by controlling, conversely, the pressurization and filling of the lowering chamber, and emptying of the lift chamber, until operation of the mechanical locking device is obtained, or by providing hydraulic locking of the lowering chamber by a pressurization and holding valve. Operation of the shock absorber at the upper part of the jack rod is provided conventionally, any compression load on the shock absorbing jack causing the shock absorber rod to be driven into the jack rod and shock absorbing of this movement by dissipation of energy through throttling of the hydraulic liquid contained in the upper chamber of the jack rod and passing through the throttling orifices of the shock absorber piston in the peripheral chamber of the shock absorber rod, while compressing therein the low pressure gas chamber which it contains. After the shock absorber rod has been driven into the jack rod, expansion of the compressed low pressure gas chamber pushes the hydraulic liquid back from the shock absorber rod to the upper chamber of the jack rod, which tends to push the shock absorber rod out of the jack rod, with braking provided by throttling of the hydraulic liquid in the throttling orifices of the flap provided for this purpose. After landing, from the undercarriage down position, the shock absorbing jack is under a static load (shock absorber rod partially entered into the jack rod), and the shock absorbing rod is caused to pass into the kneeling gear configuration by controlling emptying of the lowering chamber, under the effect of the weight of the aircraft.
In order to further reduce the size of the shock absorbing jack in the undercarriage up configuration and, in particular, so that the size in this configuration is substantially the same as in the configuration of the undercarriage under static load, the shock absorbing jack further includes a retraction piston, mounted for sealingly sliding in the lower chamber of the jack rod, and carrying a hollow sleeve which passes through the transverse wall of the jack rod, the hydraulic liquid volume contained in its upper chamber, and the shock absorber piston, this sleeve having an upper stop by which it is slidingly mounted and retained in the central chamber of the internal cylindrical wall of the shock absorber rod. The retraction piston thus defines, on the one hand with the jack piston, a vented chamber in communication through the central passage of the sleeve with the central vented chamber of the shock absorber rod, and, on the other hand, with the tranverse wall of the jack rod, a retraction chamber of the shock absorber, so that, when this retraction chamber is supplied with hydraulic liquid, at the same time as the annular lift chamber, the retraction piston is moved towards the jack piston and, through its sleeve, pulls the shock absorber rod into the jack rod. The shock absorbing jack has then its minimum size, because its jack rod has entered the jack cylinder and because the shock absorber rod has partially entered the jack rod.
This construction, in which the lowering chamber of the jack has the additional advantage of extending the shock absorbing travel, in the case of an emergency landing, forms the subject matter of improvements which are described in the first certificate of addition No. 2 370 196 of the above mentioned patent.
These improvements consist essentially in the provision, at the lower part of the jack cylinder, of an additional chamber adjacent the lowering chamber, in which the additional chamber is separated by a separator piston, returned by resilient means against a first stop, so as to limit the volume of the lowering chamber and movable against resilient means under the effect of the expansion of the hydraulic fluid in the lowering chamber, so that the additional chamber forms a chamber for accumulating the expansion not only of the hydraulic fluid in the lowering chamber, but also of the hydrualic fluid in the lift chamber and in the retraction chamber, in communication with each other, if the part of the lower chamber of the jack rod which does not form the retraction chamber is placed in communication with the lowering chamber, that is to say if the jack piston is in fact an annular piston separating the lowering and lift chambers. The additional chamber may be filled with hydraulic liquid, contain a spring applying the separator piston against a stop corresponding to the base of the lowering chamber and be in communication with an expansion valve, making possible emptying of the accumulation chamber when the separator piston is moved against the spring by expansion of the hydraulic liquid, as well as resupplying the accumulation chamber during application of a lowering pressure in the lowering chamber. But, in an advantageous variant, the additional chamber contains a presssurized gas forming simultaeously a pneumatic spring, applying the separator piston against the corresponding stop, and an additional shock absorbing chamber whose effects are added to those of the oleopneumatic shock absorber at the upper part of the jack rod. In addition, the lowering chamber is connected to an overpressure valve making is possible to empty the lowering chamber when the jack rod is subjected to a force greater than a predetermined value, so that the shock absorbing jack behaves like a shock absorber with extended travel in the case of emergency landing. Finally, in a variant which has been constructed and equips certain of the applicant's helicopters the stop against which the separator piston is applied by the high pressure gas contained in the additional chamber is in the form of a transverse dividing wall internal to the jack cylinder and having at least one orifice opening onto at least one throttling flap situated between the dividing wall and the separator piston, so as to form a second shock absorber. In this case, the retraction chamber is fed through a channel formed inside an axial sleeve, integral with this dividing wall and so with the jack cylinder and sealingly sliding in the retraction piston, this sleeve having an enlarged head which itself sealingly slides inside the sheath integral with the retraction piston and retained in abutment in the shock absrober rod. Finally, a second channel formed in the sleeve places the internal channel defined in the sheath, closed at its upper end in the shock absorber rod and extending between this upper closed end and the enlarged head of the sleeve, in communication with the hydraulic liquid chamber of the second shock absorber, that is to say the chamber defined between the transverse dividing wall of the jack cylinder and the separator piston, so that the chamber inside the retraction sheath of the shock absorber rod in the jack rod forms an extension chamber for the hydraulic liquid in the liquid chamber of the high pressure shock absorber thus formed at the base of the shock absorbing jack. Thus a shock absorbing jack is obtained equipped with two shock absorbers, one of which, at the upper part, includes a low presssure gas chamber and the other of which, at the lower part, has a high pressure gas chamber, the two shock absorbers being separated by a jack, whose cylinder receives the high pressure gas chamber, this latter being actuated from the moment when the load of the low pressure gas chamber exceeds the inflation pressure of the high pressure gas chamber.
French patent No. 2 461 852 describes other shock absorbing jack constructions, shown in FIGS. 2 to 6, and which comprise a cylindrical body with two end chambers open axially to the outside, a jack rod mounted for sealingly sliding in the lower end chamber of the cylinder, and defining by its internal face and the external face of its part engaged in the cylinder respectively a lowering chamber and a lift chamber, which are respectively fed with hydraulic liquid for controlling the extension and retraction of the jack rod from or into the cylinder, and a shock absorber rod mounted for sealingly sliding in the upper end chamber of the cylinder, and containing a low pressure gas chamber adjacent a hydraulic liquid volume in communication with the hydraulic liquid contained in the upper end chamber of the cylinder through a throttling device, with which a shock absorber piston is provided, carried by the end of the shock absorber rod inside the cylinder.
In addition, these shock absorbing jacks comprise a mobile bottom, formed as a separator piston, on which is applied the pressure of the hydraulic liquid reigning in the upper chamber of the cylinder, and itself bearing against a force threshold element formed by a high pressure gas chamber, allowing a stroke of the mobile bottom, at the time of a compression load on the shock absorbing jack, from a force greater than a given threshold, corresponding to the inflation pressure of the high pressure gas chamber, and independently of the speed at which the shock absorber rod is driven into the cylinder.
In some embodiments (FIGS. 3 and 4), the two end chambers of the cylinder are separated by a fixed transverse dividing wall, through which pass channels for placing the upper end chamber of the cylinder in communication with a subsidiary chamber in which the mobile bottom and the high pressure chamber are housed, the subsidiary chamber being either an annuar chamber of the cylinder which substantially surrounds the upper end chamber of the cylinder and in which the mobile bottom adapted as an annular piston (FIG. 3) slides or the internal chamber of a bottle or capacity external to the cylinder and in which the mobile bottom slides (FIG. 4).
In other embodiments (FIGS. 2, 5 and 6), the high pressure gas chamber is disposed in the cylinder, between the two end chambers thereof. In this case, the mobile bottom may form the bottom of the upper end chamber and the high pressure gas chamber is defined between the mobile bottom and a fixed transverse dividing wall of the cylinder, which forms the bottom of the lower end chamber (FIG. 2). Furthermore, a separator piston is advantageously mounted for sealingly sliding inside the jack rod for separating the lowering chamber, thus defined in the jack rod, from the adjacent volume of hydraulic liquid retained in the lower end chamber of the cylinder and in communication with the hydraulic liquid of the upper end chamber through a hollow rod which is carried by the transverse dividing wall, passes through the high pressure gas chamber and about which the mobile bottom is mounted for sealingly sliding (FIG. 5). Finally, it is possible for the bottom of the upper end chamber to be formed by the fixed transverse dividing wall of the cylinder, whereas the bottom of the lower end chamber is formed by the mobile bottom, separating the high pressure gas chamber housed between the mobile bottom and the fixed dividing wall, of the hyraulic liquid volume contained in the lower end chamber and in communication with the liquid of the upper end chamber through the hollow rod carried by the fixed dividing wall (FIG. 6).
In these different constructions, a retraction piston is mounted for sealingly sliding in the upper end chamber and about the part of the shock absorber rod which is engaged in the cylinder, and this retraction piston defines a retraction chamber which, when it is supplied with pressurized hydraulic liquid, controls the retraction of the shock absorber rod into the cylinder by means of the retraction piston. Similarly, retraction of the jack rod into the cylinder may be provided by another retraction piston, mounted for sealingingly sliding in the lower end chamber and about the part of the jack rod which is engaged in the cylinder so as to define the retraction chamber.
French patent No. 2,493,444 concerns improvements made to the shock absorber part of devices such as the shock absorbing jacks forming the subject of the above mentioned patents. These improvements consist essentially in an additional separator piston mounted for sealingly sliding inside the shock absorber rod and separating the low pressure gas chamber, at the lower part in this rod, from a hydraulic liquid volume, at the top part in this rod, and a hydraulic distributor block, external to the shock absorber, is in communication with the top part of the shock absorber rod, so as to cause the hydrualic liquid volume which it contains to vary, the separator piston sealingly sliding about a hollow axial rod, internal to the shock absorber rod, and causing the low pressure gas chamber to communicate with a connection duct to a pressurized gas source. Furthermore, the hydraulic distributor block controls the emptying of the hydraulic liquid from the top part inside the shock absorber rod when this latter is urged by the corresponding retraction piston and is driven into the cylinder. Finally, French patent No. 2,554,415 provides a shock absorber jack for landing gear which allows lowering under the effect of the weight of the aircraft itself and return to the "undercarriage down" position on the ground, but which does not fulfill the function of a jack providing lifting or retraction of the landing geaer during flight. In fact, this patent relates specifically to a forward and orientable landing gear equipped with a shock absorbing jack having a single low pressure gas chamber and which is mounted in a case pivoting on the structure of the aircraft, so as to make possible the up or down position of the front landing gear by pivoting about a transverse and fixed shaft of the structure, and not by reduction of the axial dimension of the shock absorbing jack.
The shock absorbing jack comprises a rod, formed of two coaxial tubes o different sections, connected together by a bottom at one of their ends, a cylinder with closed bottom, containing hydraulic liquid and sliding between the two tubes and whose open end engaged between the two tubes forms an annular piston, the shock absorbing jack also comprising a throttling device carried by the end of the internal tube engaged in the cylinder, a low pressure gas chamber contained in the internal tube between a hydraulic liquid chamber in communication with the one contained in the cylinder through throttling orifices, and a separator piston sealingly sliding in the internal tube so as to separate the low pressure gas chamber from a hydraulic liquid chamber connected to a hydraulic block. The rod is mounted for axial sliding in a case which defines with the external tube a jack chamber, normally filled with hydraulic liquid, and which is emptied towards the hydraulic block, on lowering under the effect of the weight of the aircraft, so that in the lowered position, the upper part of the rod extends above the case, the return to the "undercarriage down" position under a static load on the ground, being provided by filling this chamber.
The projection of the upper part of the rod above the case, in the lowered position, is a configuration which is not admissible in main landing gear, particularly for helicopters, of the direct sliding type, in which the shock absorbing jack is housed in the shock absorber leg, like the "pendulum", in which the shock absorber rod is housed in a resilient manoeuvering strut, when the leg or the strut respectively must be slanted from the outside towards the inside and from bottom to top with respect to the vertical, longitudinal and median plane of the aircraft.
All the constructions described in the above mentioned patents have the common drawback that their structure and operating mode are complex. In particular, they include a relatively large number of pistons and other sealingly sliding members forming pistons as well as a large number of dynamic seals and, generally, a large number of mechanical components. The result is that the manufacturing, fitting and maintenance costs are high, and that the shock absorbing jacks obtained are heavy.
The problem underlying the invention consists in simplifying, to a large extent, the structure and operating principle of a shock absorbing jack, for equipping the landing gear of aircraft, in particular aircraft with rotating wings and fulfilling at one and the same time the functions of shock absorber with high energy absorption and of jack for raising and lowering the undercarriage, making possible the extra lowering and/or extra raising of the aircraft and, possibly, landing in the jack up position.